| With the rapid development of society and the continuous progress of technology, it is higher of the control of temperature controlling. In order to meet the actual real-time, on-line and accurate measurement of the actual temperature field, and being sure to the high precision and fast measurement of loose time on acoustic wave propagation path and the inversion reconstruction algorithm of temperature field in high quality. The purpose of this study is to solve the previous key technical problem.This paper embarks from the time delay estimation method, this paper proposes a kind of method for high precision and fast measurement of sound waves to loose time, it is the time delay estimation method based on pseudo-random sequence for a rough side, then utilizing the phase comparison algorithm precision. M sequence of pseudo-random sequence with good randomness and correlation function characteristics, and it is easy to find a sharp peak to obtain acoustic loose time during the cross-correlation algorithm. But this method can only solve the time of cycle times wavelength in integer. For the cycle times wavelength in non-integer period part, and ensuring to measure acoustic loose time in a high precision. Due to the computation of the DFT algorithm is too large and the measurement time is more longer in the phase comparison algorithm, so choosing the FFT algorithm in order to guarantee of the rapid measurment the acoustic travel time.Through the research, the experimental system is designed based on the method presented in this paper is that 40 KHz square wave pulse is selected as carrier signal, and M sequence is generated by level 7 shift register is selected as pseudo-random sequence. The two signals are modulated by using 2ASK, and they are launched by emitting transducer after amplification, the signal received by receiving transducer are processed on amplification, filtering, shaping and normalization, the first correlation processing, then completing the rough side. Doing DFT transform for a sequence of discrete in the cycle times wavelength in non-integer period part, and the discrete sequence phase is obtained based on the relationship of the ratio of the imaginary part and the real part and the phase angle in the DFT transform, then finishing the fine side. Designing the related circuit, the sampling frequency is 200 kHz is the best when the carrier signal frequency is 40 kHz is determined through simulation. The Sampling points in the FFT algorithm is 1024.Under laboratory conditions, and using the above-mentioned measured acoustic loose time system with air as the gas medium by control variables method for experiments. In the conditions of The different propagation distance(certain SNR) and different SNR(certain propagation distance) respectively, and multiple measurements of acoustic travel time. The Experimental results shows that, at first, under the certain SNR, the measured absolute measurement error tended to increase with the increase of distance measurement, while the relative error is swing, and the development tendency is not obvious. However, under the certain propagation distance, the measured absolute measurement error reduced gradually with the increase of SNR, while the relative error tended to reduce. Secondly, the gas medium temperature have a modest influence on the measuring result. Thirdly, under the certain SNR, the absolute measurement error is less than 10 s when the distance measurement is less than 3m, the measured relative error is superior to 1! when the distance measurement is more than 3m, it basically meets the expected experiment goal. Single path measurement time meets the intended target, that is to say, single path measurement time is less than 20 ms. Finally, compared with the time delay estimation method of pseudo-random sequence, the method of the measurement accuracy is proposed in this paper is improved by 3 times. While Compared with other traditional measurement methods, it has a significant advantage. |
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